1. Field of the Invention
This invention relates generally to gas separation by electrostatic precipitators and more particularly to an electrostatic precipitator having a discharge electrode assembly stabilizing means for maintaining discharge electrode wires substantially centered between adjacent collector electrodes.
2. Description of the Prior Art
Removal of particles from a gas stream by plate type electrostatic precipitators is well known in the art. In such precipitators, a particle laden gas flows through an inlet port in the precipitator shell; into a gas chamber in the electrostatic precipitator, and through gas passages which are formed between laterally spaced rows of vertical collector electrodes suspended within the gas chamber. Suspended in each of the gas passages between adjacent collector electrodes are a plurality of discharge electrode wires which are electrically insulated from the shell of the precipitator. As the particle laden gas passes through the gas passages between the collector electrodes, the discharge electrode wires are energized, creating an electrostatic field around each discharge electrode wire which ionizes the particles in the gas. The ionized particles are then attracted to and collected on the collector electrodes. The collector electrodes are then rapped to dislodge the particles therefrom and the particles fall to the bottom of the precipitator into collection hopper from where they are disposed of outside the precipitator system.
It has been found that the electrostatic field surrounding the discharge electrode wires tends to oscillate the wires within the gas passages. As the wires oscillate, they come within close proximity to adjacent collector electrodes. When the wires come too close to a collector electrode, arcing will occur between the wire and the collector electrode. Such arcing is detrimental to the operation of the precipitator system because it reduces the strength of the electrostatic field surrounding the discharge wires and thus decreases the efficiency of the system. In addition, it causes damage to the collector electrodes and the discharge electrode wires. For this reason, it is desirable to maintain the wires within the gas passages without any significant oscillation.
To help prevent oscillation of the discharge wires, weights are usually attached to the bottom of the wires. The weights tend to keep the wires straight because they present a greater mass for the electrostatic field to overcome in order to oscillate the wires. For many years the use of weights attached to the bottom of the wires was satisfactory because the electrostatic fields used were relatively weak and the discharge wires were relatively short. However, in modern electrostatic precipitators, high strength electrostatic fields are common and the discharge wires are much longer so that oscillation of the wires still occurs even with weights attached. To counteract this oscillation, a weight guide grid system is now used, being suspended below the bottom of the collector electrodes from a top frame supporting the discharge electrode wires thereby insulating the grid from the shell of the precipitator. The bottom grid system is arranged so that the weights from the wires are suspended within the grid system. The grids prevent the discharge wires and weights from oscillating to a limited degree. However, the size of electrostatic precipitators continues to be increased and collector electrodes 24 to 35 feet or longer are common. The discharge electrode wires are even longer than the collector electrodes and may be from 24 to 35 feet or longer. With wires this long, it has been found that even with a rigid weight guide grid frame suspended beneath the collector electrodes, the electrostatic fields are so strong that the entire wire and grid system tend to swing and thus the same problem develops in that arcing occurs between the wires and the collector electrodes.
One method now used to prevent the bottom weight guide grid frame and discharge wires from swinging is to anchor the bottom weight guide grid frame to the wall of the electrostatic precipitator hopper which is located below the collector electrodes. Insulators must be used to anchor the grid since the wall of the hopper is at a different potential than the discharge wires and bottom weight guide grid system. Although anchoring the bottom weight guide grid frame to the hopper wall prevents the frame from oscillating, it does have a number of disadvantages.
One disadvantage of the above system is that the insulators are located below the hot gas stream and the temperature below the collector electrode plates may go below the dew point. If this happens, condensation will form on the insulators which may cause an electrical short between the discharge wires and the hopper resulting in a break down of the electrostatic precipitator. In addition, since the insulators are located below the collector electrodes, dust building up in the collection hopper may reach the insulator and result in an electrical short. Another disadvantage of anchoring the bottom weight guide grid frame to the hopper is that it is at a different temperature than the hopper which is below the hot gas stream while the weight guide grid frame is within the hot gas stream. Thus, there is considerable difference in the thermal expansion between the hopper and the bottom weight guide grid frame. This difference tends to pull the weight guide grid frame out of alignment and closer to one of the collector electrodes. When this happens, arcing may occur.
Another system used to prevent the discharge electrode wires and bottom weight guide grid frame from swinging consists of a number of rigid trusses between the top discharge electrode support frame and the bottom weight guide grid frame. Out of necessity, these trusses must be extremely large. Since the space between the collector electrodes is relatively small, at least one collector electrode section must be removed from the system in order to use a truss big and strong enough to prevent swinging. Since a number of these trusses must be used, a number of collector electrode sections must be removed. Removing the collector plates is undesirable since spaces will be left where no particles will be collected. In addition, trusses must be used which are of 24 to 35 feet or more in length and are extremely expensive. Since the two above described methods of preventing the discharge electrode wires and bottom weight guide grid frame from oscillating has proved to be ineffective or far too expensive, a new and inexpensive system is needed to overcome the above problems.